What is fogging test in eye examination ?
This technique is used to find out the maximum correction, a hyperopic person can be prescribed.
Patient is made to sit with both the eyes open, after adding nearly full hyperopic cycloplegic correction in the trial frame.
He is asked to look at a distant object to relax his accommodation and called in after 15-20 minutes. The power is reduced by adding minus lenses till he can see clearly.
For Example:
Present Prescription: RE: + 1.0 DS, LE: + 1.0 DS
Non Cycloplegic AR: RE: + 2.0 DS, LE: + 2.0 DS
Cycloplegic AR: RE: + 8.0 DS, LE: + 8.0 DS
First, add + 8.0 DS lens in the trial frame in both the eyes and make the patient wait outside with both the eyes, looking at a distant object for 15-20 mins.
Now, call the patient inside and check his/her vision.
If the patient’s vision is less than 6/18 with both eyes open, try fogging with +6.0 DS both eyes and keep on reducing the power of the lenses till you get around 6/18.
Now, with both eyes open keep on adding minus lenses in front of both the eyes, till vision becomes 6/6.
y Usually by reducing the number by +1DS or + 2DS, the patient should be able to read 6/6.
Fogging depends on the following parameters:
i. The cycloplegic AR
ii. The difference between the cycloplegic and the non-cycloplegic AR. If this difference is more, the patient is accommodating a lot and we will not be able to fog with full cycloplegic AR.
iii. The difference between cycloplegic AR and the present glass prescription.
iv. The age of the patient. This determines the effort required for a maximum tolerable hyperopic prescription.